/*

 * Licensed to the Apache Software Foundation (ASF) under one

 * or more contributor license agreements.  See the NOTICE file

 * distributed with this work for additional information

 * regarding copyright ownership.  The ASF licenses this file

 * to you under the Apache License, Version 2.0 (the

 * "License"); you may not use this file except in compliance

 * with the License.  You may obtain a copy of the License at

 *

 *     http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package com.bff.gaia.unified.runners.core;



import com.bff.gaia.unified.sdk.state.TimeDomain;

import com.bff.gaia.unified.sdk.transforms.DoFn;

import com.bff.gaia.unified.sdk.transforms.windowing.BoundedWindow;

import com.bff.gaia.unified.sdk.util.WindowedValue;

import com.bff.gaia.unified.sdk.values.PCollectionView;

import com.bff.gaia.unified.vendor.guava.com.google.common.collect.ImmutableList;

import com.bff.gaia.unified.vendor.guava.com.google.common.collect.Iterables;

import org.joda.time.Instant;



import javax.annotation.Nullable;

import java.util.Collection;

import java.util.Collections;

import java.util.HashSet;

import java.util.Set;



/**

 * A {@link DoFnRunner} that can refuse to process elements that are not ready, instead returning

 * them via the {@link #processElementInReadyWindows(WindowedValue)}.

 */

public class SimplePushbackSideInputDoFnRunner<InputT, OutputT>

    implements PushbackSideInputDoFnRunner<InputT, OutputT> {

  private final DoFnRunner<InputT, OutputT> underlying;

  private final Collection<PCollectionView<?>> views;

  private final ReadyCheckingSideInputReader sideInputReader;



  // Initialized in startBundle()

  private @Nullable

  Set<BoundedWindow> notReadyWindows;



  public static <InputT, OutputT> SimplePushbackSideInputDoFnRunner<InputT, OutputT> create(

      DoFnRunner<InputT, OutputT> underlying,

      Collection<PCollectionView<?>> views,

      ReadyCheckingSideInputReader sideInputReader) {

    return new SimplePushbackSideInputDoFnRunner<>(underlying, views, sideInputReader);

  }



  private SimplePushbackSideInputDoFnRunner(

      DoFnRunner<InputT, OutputT> underlying,

      Collection<PCollectionView<?>> views,

      ReadyCheckingSideInputReader sideInputReader) {

    this.underlying = underlying;

    this.views = views;

    this.sideInputReader = sideInputReader;

  }



  @Override

  public DoFn<InputT, OutputT> getFn() {

    return underlying.getFn();

  }



  @Override

  public void startBundle() {

    notReadyWindows = new HashSet<>();

    underlying.startBundle();

  }



  @Override

  public Iterable<WindowedValue<InputT>> processElementInReadyWindows(WindowedValue<InputT> elem) {

    if (views.isEmpty()) {

      // When there are no side inputs, we can preserve the compressed representation.

      underlying.processElement(elem);

      return Collections.emptyList();

    }

    ImmutableList.Builder<WindowedValue<InputT>> pushedBack = ImmutableList.builder();

    for (WindowedValue<InputT> windowElem : elem.explodeWindows()) {

      BoundedWindow mainInputWindow = Iterables.getOnlyElement(windowElem.getWindows());

      if (isReady(mainInputWindow)) {

        // When there are any side inputs, we have to process the element in each window

        // individually, to disambiguate access to per-window side inputs.

        underlying.processElement(windowElem);

      } else {

        notReadyWindows.add(mainInputWindow);

        pushedBack.add(windowElem);

      }

    }

    return pushedBack.build();

  }



  private boolean isReady(BoundedWindow mainInputWindow) {

    if (notReadyWindows.contains(mainInputWindow)) {

      return false;

    }

    for (PCollectionView<?> view : views) {

      BoundedWindow sideInputWindow = view.getWindowMappingFn().getSideInputWindow(mainInputWindow);

      if (!sideInputReader.isReady(view, sideInputWindow)) {

        return false;

      }

    }

    return true;

  }



  @Override

  public void onTimer(

      String timerId, BoundedWindow window, Instant timestamp, TimeDomain timeDomain) {

    underlying.onTimer(timerId, window, timestamp, timeDomain);

  }



  @Override

  public void finishBundle() {

    notReadyWindows = null;

    underlying.finishBundle();

  }

}